On the origin of the so called conical emission in laser pulse propagation in atomic vapor

Propagation in Na vapor of a near resonant pulse from a single mode tunable dye laser is shown to produce, among other effects, a forward coherent, broadband (0.2 nm) scattering with two apparent spectral maxima which can be observed for both detuning sides of the laser frequency with respect to the atomic frequency. The spectral angular distribution of the scattering is studied. The origin of the broadening is suggested to be a combination of stimulated Raman scattering and self phase modulation. It is proposed that the red wing of this emission, which was previously observed only in a ring (and often referred to as "the conical emission") can be interpreted, as well as the new observation reported here, as part of a more general process involving reabsorption of the generated near resonant broadband which, because of self lensing processes, is angularly dispersed.